This application is the national phase under 35 U.S.C. xc2xa7371 of PC International Application No. PC/JP02/01863 which has an International filing date of Feb. 28, 2002, which designated the United States of America.
1. Technical Field
This invention relates to a reflector antenna apparatus, and in particular it relates to a reflector antenna apparatus which can perform scanning by pivoting about two axes which are perpendicular to each other.
2. Background Art
An example of a reflector antenna apparatus which can perform scanning by pivoting about two axes which are perpendicular to each other such as an azimuth axis and an elevation axis is that described, for example, in xe2x80x9cProceedings of ISAP2000xe2x80x9d, pages 497-500, Japan, by H. Wakana et al. That reflector antenna apparatus is a normal axially symmetric Cassegrain antenna in which the reflector has a subreflector which receives irradiation of electromagnetic waves from a radiator and a main reflector which reflects electromagnetic waves which are reflected from the subreflector and directs them at a target. Not only the height dimensions in the direction of the azimuth axis of the reflector antenna apparatus but also the lengthwise dimensions in the direction of the elevation axis and the widthwise dimensions in the direction perpendicular thereto are large. In addition, the central axis of elevation rotation does not pass through the reflector but passes through a location spaced from the reflector, so if the direction (angle) of the reflector is changed, its position necessarily changes, so it is necessary to provide a large operating space for the reflector of the antenna apparatus, and a large space was necessary for installing the reflector apparatus.
When it is required to install a reflector antenna apparatus in a limited, relatively small space such as when mounting one on an aircraft, a conventional reflector antenna apparatus could not be employed because, as described above, it has a large reflector operating region. It has also been proposed to arrange an array of small antenna elements in a fixed location and decrease height dimensions and to perform scanning by electrically controlling the directionality of the antenna elements, but a control apparatus for electrically controlling such an antenna apparatus becomes extremely expensive, so that proposal has almost no practicality.
Accordingly, an object of this invention is to provide a reflector antenna apparatus which can be installed in a small space, which has sufficient practicality, and which can perform scanning by pivoting about two axes which are perpendicular with respect to each other.
According to the present invention, means for solving the above-described problems are as follows.
(1) A reflector antenna apparatus having a reflector and a rotating mechanism which rotates the reflector about an azimuth axis and an elevation axis, characterized in that the elevation axis passes through a location at substantially the center of the reflector in the direction of the azimuth axis and through substantially the center of the reflector in the direction perpendicular to the elevation axis, and the reflector has a substantially rectangular aperture which is elongated in the direction of the elevation axis, and the reflector has its reflector surface adjusted so as to receive and reflect substantially all of the supplied electromagnetic waves, whereby the antenna height does not become large when the reflector rotates about the elevation axis.
(2) The reflector may have a subreflector which receives electromagnetic waves irradiated by a radiator and a main reflector which reflects electromagnetic waves which are reflected from the subreflector and directs them towards a target.
(3) A portion of a current supply apparatus which rotates at the same time as the reflector antenna may be included in the reflector so that the antenna height does not become large.
(4) The reflector may be a reflector array having a plurality of reflector elements which are arranged in alignment with the elevation axis.
(5) Each of the reflector antennas of the main reflector has a substantially rectangular aperture, and reflector surface adjustment may be carried out so as to form a reflector antenna in which when each reflector antenna is viewed in the direction of the reflector axis, the aperture is rectangular and the electromagnetic field distribution in the aperture is nearly uniform so as to suppress grating lobes.
(6) It is one in which the reflector surface is set so that the radiator is parallel to the azimuth rotational surface, and the center of the central axis of the reflector is aligned with the elevation axis.
(7) It is one in which the reflector surface is set so that the subreflector is not blocked as viewed from the reflector axis.
(8) The reflector antenna is a Cassegrain antenna.
(9) The reflector antenna is a Gregorian antenna.